分类： 物理学 >> 核物理学 提交时间： 2023-09-07
摘要： Heliumxenon cooled microreactors are a vital technological solution for portable nuclear reactor power sources. To examine the convective heat transfer behavior of heliumxenon gas mixtures in a core environment, numerical simulations are conducted on a cylindrical coolant channel and its surrounding solid regions. Validated numerical methods are used to determine the effect and mechanisms of power and its distribution, inlet temperature and velocity, and outlet pressure on the distribution and change trend of the axial Nusselt number. Furthermore, a theoretical framework that can describe the effect of power variation on the evolution of the thermal boundary layer is employed to formulate an axial distribution correlation for the Nusselt number of the coolant channel, under the assumption of a cosine distribution for the axial power. Based on the simulation results, the correlation coefficients are determined, and a semi-empirical relationship is identified under the corresponding operating conditions. The correlation derived in this study is consistent with the simulations, with an average relative error of 5.3% under the operating conditions. Finally, to improve the accuracy of the predictions near the entrance, a segmented correlation is developed by combining the Kays correlation with the aforementioned correlation. The new correlation reduces the average relative error to 2.9% and maintains satisfactory accuracy throughout the entire axial range of the channel, thereby demonstrating its applicability to turbulent heat transfer calculations for heliumxenon gas mixtures within the core environment. These findings provide valuable insights into the convective heat transfer behavior of a heliumxenon gas mixture in a core environment.
分类： 核科学技术 >> 核科学与技术 提交时间： 2023-09-06
摘要： The accurate modeling of depletion, intricately tied to the solution of the neutron transport equation, is crucial for the design, analysis, and licensing of nuclear reactors and their fuel cycles. This paper introduces a novel multi-group Monte-Carlo depletion calculation approach. Multi-group cross-sections (MGXS) are derived from both 3D whole-core modeling and a 2D fuel subassembly using the continuous-energy Monte-Carlo technique. Core calculations employ the multi-group Monte-Carlo method, accommodating both homogeneous and specific local heterogeneous geometries. The proposed method has been validated against the MET-1000 metal-fueled fast reactors, using both the OECD/NEA benchmark and a new refueling benchmark introduced in this paper. Our findings suggest that microscopic MGXS, produced via the Monte-Carlo technique, are viable for fast reactor depletion analyses. Furthermore, the locally heterogeneous model with angular-dependent MGXS offers robust predictions for core reactivity, control rod value, sodium void value, Doppler constants, power distribution, and concentration levels.
分类： 核科学技术 >> 辐射防护技术 提交时间： 2023-06-06
摘要： The uncertainty of nuclide libraries in the analysis of the gamma spectra of low- and intermediate-level radioactive waste (LILW) using existing methods produces unstable results. To address this problem, a novel spectral analysis method is proposed in this study. In this method, overlapping peaks are located using a continuous wavelet transform. An improved quadratic convolution method is proposed to calculate the widths of the peaks and establish a fourth-order filter model to estimate the Compton edge baseline with the overlapping peaks. Combined with the adaptive sensitive nonlinear iterative peak, this method can effectively subtracts the background. Finally, a function describing the peak shape as a filter is used to deconvolve the energy spectrum to achieve accurate qualitative and quantitative analyses of the nuclide without the aid of a nuclide library. Gamma spectrum acquisition experiments for standard point sources of Cs-137 and Eu-152, a segmented gamma scanning experiment for a 200 L standard drum, and a Monte Carlo simulation experiment for triple overlapping peaks using the closest energy of three typical LILW nuclides (Sb-125, Sb-124, and Cs-134) are conducted. The results of the experiments indicate that (1) the novel method and gamma vision (GV) with an accurate nuclide library have the same spectral analysis capability, and the peak area calculation error is less than 4%; (2) compared with the GV, the analysis results of the novel method are more stable; (3) the novel method can be applied to the activity measurement of LILW, and the error of the activity reconstruction at the equivalent radius is 2.4%; and (4) The proposed novel method can quantitatively analyze all nuclides in LILW without a nuclide library. This novel method can improve the accuracy and precision of LILW measurements, provide key technical support for the reasonable disposal of LILW, and ensure the safety of humans and the environment.
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